1. Field of the Invention
The present invention relates to an air conditioning system in which the rotational speed of a compressor is varied in response to the operation instructions from indoor units.
2. Prior Art
There has been devised and demonstrated an air conditioning system (to be referred to as "a multi-air-conditioning system" in this specification) in which one outdoor unit drives a plurality of indoor units. Such air conditioning systems have been widely used in urban areas because the installation space for an outdoor unit can be reduced. However, depending upon the number of indoor units to be driven, the air conditioning load varies widely so that the capacity control of a compressor of an outdoor unit is required. In this specification, the air conditioning load refers to a heating load, a cooling load and a load required for controlling the humidity.
In the conventional air conditioning systems, a pole change compressor has been used in order to control the capacity of the compressor. However, the pole change compressor is such that it can be only switched between two poles and four poles. As a result, the compressor can respond to some variation in air conditioning load, but cannot sufficiently control the indoor units in response to the load variation due to variation in temperature in each room and in the number of operating indoor units.
There has been also devised and demonstrated a system in which an inverter is used to control a compressor. That is, the output frequency of the inverter is varied so that the capacity of the compressor is varied. However, there has not been proposed a multi-air-conditioning system in which in response to the operation instructions derived from indoor units an optimum frequency is determined so as to control the inverter.